Probing Electronic Spectra Step-By-Step

A newly developed scanning probe method can induce a sequence of bond-selective chemical reactions in individual complex molecules. The technique also monitors the resulting evolution of electronic spectra at select positions within the molecule at each step in the reaction sequence (Nat. Chem., DOI: 10.1038/nchem.1488). The method may provide key data needed to understand electronic properties of molecules that underpin molecular electronic devices. By tuning the energy of electrons injected at target points in a π-conjugated molecule known as DSB-2S-2Ac, Ying Jiang and Wilson Ho of the University of California, Irvine, and coworkers selectively and sequentially cleaved two acetyl groups and two sulfur atoms from roughly 50 of these molecules. After each dissociation step, the team recorded current-voltage profiles at select points within the molecules to determine, for example, how breaking a bond at one end of the molecule affects electronic conductivity at the other end. The team also scrutinized site-specific electronic effects of bond formation as they selectively induced gold atoms to form gold-sulfur linkages in a related molecule.